In JP 2002-13547A, a known torque fluctuation absorbing apparatus is disclosed. A damper for a hybrid type driving device is disclosed in JP2002-13547A, and the damper has a limiter mechanism in addition to a damper mechanism. The damper mechanism absorbs driving torque fluctuations of a flywheel fixed to a driving shaft of a driving source, and the limiter mechanism is disposed on a radially outward portion of the damper mechanism. The limiter mechanism is configured by crimping friction materials with the flywheel directly or indirectly (via a frictional surface plate). The friction material is fixed to the outer circumference of the damper mechanism. When fluctuating torque reaches a predetermined value (limit torque value), the limiter mechanism allows sliding of the damper mechanism to prevent excessive torque from being input to a transmission.
Further, in JP2003-194095A, another torque fluctuation absorbing apparatus is disclosed. The torque fluctuation absorbing apparatus is configured so as to prevent the foreign objects such as dust from adhering to the limiter mechanism considering the exposure of the limiter portion to the outer atmosphere during transportation. In addition, in JP2003-194095A, it is suggested that a slit is formed to communicate a radially inward portion with a radially outward portion in the friction material of the limiter mechanism as a part of measures for adhesion of foreign objects.
However, in the known torque fluctuation absorbing apparatus described above, the limit torque value is subject to change due to rust, corrosion and other deteriorations which are caused by moisture and intrusion of water and other liquid from the outside after the shipment.
In JP 2003-194095A, a slit, which communicates with the radially inward portion with the radially outward portion of the friction material, is formed in the friction material of the limiter mechanism for the stabilization of the limit torque value. However, in order to retain the limit torque value with higher precision, factors (water, sand, dust and other foreign substances) for the corrosion which can intrude from the radially inward side of the friction material should be considered.
The present invention has been made in view of the above circumstances, and provides a torque fluctuation absorbing apparatus which eliminates factors causing the corrosion of a limit mechanism and stabilizes a limit torque value over a long duration.